20 HP air compressors: rotary screw becomes the default

At 20 HP the catalog flips. Below this size most buyers still pick a two stage piston; at 20 HP and up almost everything sold is a rotary screw, with duplex piston sets and oil free scroll filling the special cases. A 20 HP screw delivers 78 to 106 CFM depending on pressure and drive type, enough for a 15 to 20 bay dealership, a production machine shop, a cabinetry plant with a CNC router and a finishing room, or a mid size fabrication plant. Three phase power is assumed at this size.

What is on this page

Fixed speed rotary screw: Atlas Copco GA15-30 series (GA18 at 85 to 101 CFM from 100 to 175 PSI), Atlas Copco G15L-22 (G18 at 78 to 93 CFM), Atlas G7L-15 at 63 CFM, Chicago Pneumatic QRS 20 at 55 to 82 CFM, Chicago Pneumatic CPBg 20 gear drive at 88 CFM, and Quincy QGS 20 at 125 PSI. Variable speed: Atlas Copco GA18 VSDS at up to 106 CFM, Chicago Pneumatic CPVSd 20 at 102 CFM and Quincy QGSV-20 and QGSV-20S at 53 to 72 CFM and 175 PSI. Duplex piston: Quincy QT duplex Pro and Max (two 10 HP pumps, 14 configurations), Champion Duplex R-Series, Chicago Pneumatic RCP-C Iron duplex at 70 CFM, ABAC ABC10 Ironman duplex on 120 and 200 gallon horizontal tanks at 64 CFM, and Atlas Copco CR Industrial duplex at 73 CFM. Simplex piston: Champion R-Series 20 HP horizontal and base mounted at 78 CFM and 175 PSI, and Mark IronAir. Oil free scroll: Atlas Copco SF+ 20 at 58 CFM, Quincy QOF 20 at 55 CFM, and Chicago Pneumatic COAIRE CSOF-S 20.

Fixed speed, variable speed or duplex

Fixed speed screws cost the least and are the right choice when the plant draws close to full output most of the shift. Variable speed (VSD, VSDS, CPVSd, QGSV) tracks demand and saves 20 to 35 percent on power in plants where usage swings between shifts or between machines. A duplex piston set is the fallback for sites that need built in redundancy and cannot justify two screws; the two pumps alternate and either can carry a reduced load alone. If noise matters on the floor, the screws run 66 to 72 dBA, the duplex pistons 80 dBA or more.

Power, receiver and dryer

Plan on 54 amps at 230 volt three phase or 27 amps at 460 volt, with a magnetic starter or the packaged VSD controller. A 20 HP fixed speed screw wants a 200 to 240 gallon receiver; a variable speed unit runs well on 120 gallons. Size the refrigerated air dryer at 100 to 125 CFM and add an aftercooler if the compressor is not tank mounted with one built in.

Related pages

• 15 HP air compressors
• 25 HP air compressors
• 15 to 30 HP air compressors
• 80 CFM air compressors and 100 CFM air compressors
• 20 to 50 HP rotary screw air compressors
• Shop by HP, Shop by CFM and Shop by PSI